Particulate Fluids Processing Centrè, Department of Chemical & Biomolecular Engineering, University of Melbourne, Vic. 3010, Australia.
Langmuir. 2012 May 22;28(20):7897-903. doi: 10.1021/la3010486. Epub 2012 May 11.
A novel electrokinetic streaming potential technique has been used to determine the ζ potential behavior of three magnetic iron oxides, (Fe(3)O(4), γ-Fe(2)O(3), and CoFe(2)O(4)) as a function of pH and salt concentration. These colloidal materials, (nanosize in one dimension), are held in the form of a plug by means of external magnets. The streaming potential (E) is measured as a function of fluid flow induced by a pressure drop (ΔP) across the plug. The magnetically held plug is found to obey the requirements of the streaming potential technique; in each case an iso-electric point, (iep) independent of salt concentration is observed. However, if one uses the appropriate quantities in the standard formula, the calculated ζ potentials are very much lower than for oxides such as silica, alumina or goethite and other colloidal oxide, latex, etc. particulates in aqueous salt solutions. Furthermore, at a given pH, the measured ζ potentials anomalously increase in magnitude rather than decrease as observed conventionally as the salt concentration is increased. This apparent anomalous behavior could not be eliminated by incorporating surface conductance effects. However by including a conductance pathway, independent of pH or salt concentration, through the magnetic particle network itself, the anomaly was removed. Confirmation of the role of a conductance pathway through the magnetic particle network was obtained by using silica coated magnetic particles which displayed normal electrokinetic behavior. Finally, we have redesigned the plug-electrode assembly to allow measurement of streaming current, a technique know to eliminate contributions from plug network conductances of any kind. The resulting ζ potentials, derived from this streaming current technique are normal.
一种新型的电动流动电势技术已被用于确定三种磁性氧化铁（Fe3O4、γ-Fe2O3 和 CoFe2O4）的ζ 电位行为，其取决于 pH 值和盐浓度。这些胶体材料（一维纳米尺寸）通过外部磁铁以塞子的形式保持。通过在塞子上施加压力差（ΔP）来诱导的流体流动来测量流动电势（E）。发现磁性保持的塞子符合流动电势技术的要求；在每种情况下，都观察到与盐浓度无关的等电点（iep）。然而，如果在标准公式中使用适当的量，计算出的 ζ 电位远低于二氧化硅、氧化铝或针铁矿等胶体氧化物以及其他胶体氧化物、乳胶等在水盐溶液中的粒子。此外，在给定的 pH 值下，测量到的 ζ 电位异常增大，而不是像传统观察到的那样随着盐浓度的增加而减小。这种明显的异常行为不能通过包含表面电导效应来消除。然而，通过在磁粒子网络本身中包含一个独立于 pH 值或盐浓度的电导途径，可以消除这种异常。通过使用涂有二氧化硅的磁性粒子来证实磁粒子网络中存在电导途径的作用，这些磁性粒子表现出正常的电动行为。最后，我们重新设计了塞子-电极组件，以允许测量流动电流，这是一种已知的技术，可以消除任何类型的塞子网络电导的贡献。从这种流动电流技术得出的 ζ 电位是正常的。
